Formed when sodium chloride crystals are dissolved in water, brine is widely used in both home and industry. Ready supplies of brine of dependable concentration and in large quantity are much in demand.
The prior art describes numerous combinations for producing brine, as well as other aqueous salt solutions, of substantially constant density. In each of them, water is fed into a stationary vat in such a way that it flows through a single bed of salt, gradually dissolving it. The water feed rate and the depth of the salt bed determine the density of the salt solution which is produced. As the salt bed is consumed, this density falls unless the water feedrate is also reduced. But lowering this feedrate decreases the salt dissolving capacity of the apparatus as well. A popular remedy has been to insure steady-state operation by charging the vat continuously with crystalline salt at a rate sufficient to replenish dissolved salt.
For example, Courthope, in U.S. Pat. No. 1,928,008, patented Sep. 26, 1933, teaches this remedy. Specifically, Courthope discloses a process in which water is sprayed into a vat over a bed of rock salt. The vat includes a conically-shaped lower section above which is mounted a false bottom. Lodged thereon, the bed of rock salt filters newly formed brine as it flows downwardly en route to a valve fluidly connected to the lower section. To deliver a brine of substantially constant density, Courthope has the vat in his apparatus charged with a continuous stream of salt.
A modification of Courthope""s salt dissolving process is described in U.S. Pat. No. 2,281,140, which issued Apr. 28, 1942. There Courthope et al. disclose a machine having a screen on which a bed of rock salt is supported. Water is fed to the lower portion of this bed and drawn off above it, as salt is fed continuously into the machine, a xe2x80x9ccommon practice in the artxe2x80x9d according to Courthope et al.
Likewise, Swartz, in U.S. Pat. No. 2,412,106, which issued on Dec. 3, 1946, discloses a method for dissolving salt in which salt is fed from a hopper into a dissolving tank. The salt feedrate is sufficient to maintain a salt bed with both uniform and constant depth. From a grid of inlet pipes mounted in the bottom of a tank, water flows upwardly through the salt bed, dissolving the salt. An overflow pipe situated near the top of this tank is used to direct the salt solution into an adjacent tank for storage.
Swartz, in U.S. Pat. No. 2,576,315, patented Nov. 27, 1951, teaches a modification of his earlier disclosed process in which water is introduced both at the bottom of a tank partially filled with salt and through inlet ports located above the salt bed. An effluent which has a salt concentration dependent upon the relative flow rates of these two inlet sources is produced. As a condition for controlling Swartz"" process, the flow which passes upwardly through the bed must emerge as a saturated salt solution. To insure such a result, Swartz teaches that a minimum depth of salt bed must be maintained at all times.
Subsequent improvements in the prior art included the addition of a process step in which insoluble particles and undissolved salt particles are filtered from the brine with the use of a gravel bed. By 1967, gravel bed filters situated in salt dissolving tanks had become conventional practice according to Heiss et al. in U.S. Pat. No. 3,307,914.
The primary object of the present invention is to provide a low cost, highly efficient, and reliable salt dissolving process and apparatus which can be used to consistently provide saturated brine, even as a salt bed contained therein is being consumed, thereby allowing for full utilization of the salt bed between charges.
A further object of this invention is to provide a portable brining apparatus which can be used to supply saturated brine in quantities and at flow rates useful in industrial applications.
A still further object of the present invention is to provide such a portable brining apparatus in which the salt bed need not be replenished except at home base, thereby facilitating the transport of fresh brine to distant delivery sites.
A still further object of this invention is to provide a portable apparatus for temporarily withdrawing weak or partially saturated brine from a storage tank at a delivery site, readily concentrating this salt solution to form saturated brine, and quickly transferring the latter to said storage tank.
A still further object of this invention is to provide an improved method for quickly supplying many types and kinds of very expensive water processing systems with filtered, saturated brine.
In accordance with the present invention, there is provided an improved salt dissolving apparatus and a three stage process for utilizing this apparatus. In the first stage, water is introduced, into each of at least two tanks through a series of spray nozzles mounted near the top of each tank and around its outer periphery. The water is then passed through, in succession, beds of salt and of gravel lodged in each tank, gradually dissolving the salt, before being discharged therefrom as saturated brine. The two brine streams are then merged and subjected to a final filtration step.
In the second stage, which is triggered when at least one of the tanks by itself can no longer produce a saturated salt solution in its respective discharge stream, the method comprises introducing the discharge stream from one tank into the other tank. By fluidly connecting the two tanks together in series, the depth of the salt bed through which the water passes is effectively doubled. The second stage is continued until the two tanks so connected no longer yield a saturated brine.
In the third stage, the method comprises introducing only the discharge stream from each of the tanks into the other tank and recirculating this stream repeatedly, utilizing whatever salt bed remains to concentrate the brine until it reaches full saturation or the concentration of salt therein becomes stable over time, indicating the salt bed has been consumed.
At each stage, the salinity of the discharge streams are checked periodically using salinometers fluidly connected to the discharge lines of the two tanks.
In a preferred embodiment of the present invention, fresh water is passed through a water softener to remove any hardness therein before the water is introduced during the first stage into both tanks or, alternately, during the second stage into one tank. In a modification of this embodiment, a weak or unsaturated brine is pumped from an end user""s facility into one or both of the tanks. This unsaturated brine can also be recirculated between the two tanks using stage three of the improved method so as to concentrate the brine before final discharge.